Rising labor costs and demands for more time and cost efficient construction have made it desirable to construct building components and modules off site at specialized fabrication facilities. With wood frame structures, especially prefabricated residential structures, there are great economies to be realized by providing automated equipment that can measure and cut lumber components utilized in wall panels, roof trusses, and other prefabricated structures. Where a particular structural element is repeated over and over the use of such automated equipment can decrease construction time and lower cost. The economies of this approach are even more appealing for custom structural designs. For wood frame structures where the framing is constructed on site, precutting and marking lumber at an off site location can create a kit design minimizing measuring, sawing, and the need for specialized labor on site. This can result in faster construction as well as minimized cost. On site construction errors can also be minimized.
The use of prefabricated trusses or panels also minimizes construction delays due to the interference of bad weather at the construction site. Trusses and panels can be constructed in a controlled indoor environment without weather affecting the efficiency of the workers and equipment involved.
Prefabricated roof trusses in particular, generally include multiple pieces of lumber that must be precision cut to specific lengths as well as having precision mitered ends to form tight fitting joints. A typical roof truss includes two top chords, a bottom chord, several webs and may also include wedges and overhangs. Many of these pieces require a preparation of mitered cuts at the ends of the lumber pieces. Many of the pieces will require multiple mitered cuts on an end. For a truss to achieve its maximum structural integrity and strength the joints between the various wooden parts must be tight fitting. Thus, precision cutting of truss members is quite important to creating a truss that meets engineering standards.
In response to these needs, the process for cutting and mitering truss members, in many circumstances, has been automated for improved precision, speed and efficiency.
Prefabricated roof trusses in particular, generally include multiple pieces of lumber that must be precision cut to specific lengths as well as having precision mitered ends to form tight fitting joints. As depicted in FIG. 1, a typical roof truss includes two top chords TC, a bottom chord BC, several webs WB and may also include wedges WD and overhangs O.
As can be seen by examining FIG. 1, many of these pieces require a preparation of mitered cuts at the ends of the lumber pieces. Many of the pieces will require multiple mitered cuts on an end. For a truss to achieve its maximum structural integrity and strength the joints between the various wooden parts must be tight fitting. Thus precision cutting of truss members is quite important to creating a truss that meets engineering standards.
Thus, the process for cutting and mitering truss members, in many circumstances, has been automated for improved precision.
In particular, when cutting lumber for roof trusses some of the lumber members can be quite short. Some lumber members in roof trusses may be as short as six inches.
While currently existing automated measuring and cutting equipment can cut pieces of lumber to this length, current equipment has certain limitations. For example, once a short lumber member is cut it generally drops into a scrap bin because much currently available lumber cutting equipment has no way of conveying short lumber members once they are cut.
Another limitation of currently available automated measuring and cutting equipment is that once a single cut severing the short lumber member from a longer lumber member is made it is not possible for the automated equipment to make further cuts in that short lumber member. For example, if a 12 inch lumber member is required with two mitered cuts on each end, current automated equipment can perform the two mitered cuts on the first end without difficulty and then advance a longer section of lumber from which the short member is being cut to a position where the third cut can be made. Once the third cut is made however, the short lumber member drops into a scrap bin and is no longer available for making the fourth cut. Thus the fourth cut either must be made by hand or the short member must be manually prepared in its entirety.
Another limitation of the existing equipment is that because short lumber members are not conveyed further once they are cut but drop into the scrap bin along with true scrap pieces of material to be discarded the desired short lumber members must be sorted out by an operator from the true scraps in the bin. With very short lumber members it may be very difficult to discern what members are in fact scrap to be discarded and what lumber members are in fact usable pieces that must be retrieved.
Thus, the automated lumber cutting industry would benefit from a system for handling short pieces of lumber while still retaining the ability to make precision cuts on the short lumber members.